Near-field rf charging pad with multi-band antenna element with adaptive loading to efficiently charge an electronic device at any position on the pad

ABSTRACT

An example radio frequency (RF) charging pad includes: at least one processor for monitoring an amount of energy that is transferred from the RF charging pad to an RF receiver of an electronic device. The pad also includes: one or more transmitting antenna elements that are in communication with the processor for transmitting RF signals to the RF receiver. In some embodiments, each respective transmitting antenna element includes: (i) a conductive line forming a meandered line pattern; (ii) a first terminal of the conductive line for receiving current at one or more frequencies controlled by the processor; and (iii) one or more adaptive load terminals coupled with a plurality of respective components that allows for modifying an impedance value at each of the adaptive load terminals. In some embodiments, the processor adaptively adjusts the frequency and/or the impedance value to optimize the amount of energy that is transferred from the one or more transmitting antenna elements to the RF receiver.

RELATED APPLICATIONS

This application is a continuation-in-part application of U.S.Non-Provisional patent application Ser. No. 15/424,552, filed Feb. 3,2017, entitled “Near-Field RF Charging Pad With Adaptive Loading ToEfficiently Charge An Electronic Device At Any Position On The Pad”which claims priority to U.S. Provisional Application Ser. No.62/433,227 filed Dec. 12, 2016, the entire contents of which areincorporated herein by reference in their entireties.

This application is related to U.S. patent application Ser. No.15/269,729, filed Sep. 19, 2016, which is hereby incorporated byreference in its entirety.

TECHNICAL FIELD

The embodiments herein generally relate to antennas used in wirelesspower transmission systems and, more specifically, to a near-field RFcharging pad with adaptive loading to efficiently charge an electronicdevice at any position on the pad.

BACKGROUND

Conventional charging pads utilize inductive coils to generate amagnetic field that is used to charge a device. Users typically mustplace the device at a specific position on the charging pad and areunable to move the device to different positions on the pad, withoutinterrupting or terminating the charging of the device. This results ina frustrating experience for many users as they may be unable to locatethe device at the exact right position on the pad in which to startcharging their device.

SUMMARY

Accordingly, there is a need for wireless charging systems (e.g., RFcharging pads) that include adaptive antenna elements that are able toadjust energy transmission characteristics (e.g., impedance andfrequency for a conductive line of a respective antenna element) so thatthe charging pad is capable of charging a device that is placed at anyposition on the pad. In some embodiments, these charging pads includeone or more processors that monitor energy transferred from thetransmitting antenna elements (also referred to herein as RF antennaelements or antenna elements) and to a receiver of an electronic deviceto be charged, and the one or more processors optimize the energytransmission characteristics to maximize energy transfer at any positionon the charging pad. Some embodiments may also include a feedback loopto report received power at the receiver to the one or more processors.Such systems and methods of use thereof help to eliminate userdissatisfaction with conventional charging pads. By monitoringtransferred energy, such systems and methods of use thereof help toeliminate wasted RF power transmissions by ensuring that energy transferis maximized at any point in time and at any position at which a devicemay be placed on an RF charging pad, thus eliminating wastefultransmissions that may not be efficiently received.

(A1) In accordance with some embodiments, a radio frequency (RF)charging pad is provided. The RF charging pad includes: at least oneprocessor for monitoring an amount of energy that is transferred fromthe RF charging pad to an RF receiver of an electronic device. The RFcharging pad also includes: one or more antenna elements that are incommunication with the one or more processors for transmitting RFsignals to the RF receiver of the electronic device. In someembodiments, each respective antenna element includes: (i) a conductiveline forming a meandered line pattern; (ii) a first terminal at a firstend of the conductive line for receiving current that flows through theconductive line at a frequency controlled by the one or more processors;and (iii) a second terminal, distinct from the first terminal, at asecond end of the conductive line, the second terminal coupled with acomponent that is controlled by the at least one processor and allowsfor modifying an impedance value at the second terminal. In someembodiments, the at least one processor is configured to adaptivelyadjust the frequency and/or the impedance value to optimize the amountof energy that is transferred from the one or more antenna elements tothe RF receiver of the electronic device.

(A2) In accordance with some embodiments, a method is also provided thatis used to charge an electronic device through radio frequency (RF)power transmission. The method includes: providing a transmittercomprising at least one RF antenna. The method also includes:transmitting, via at the least one RF antenna, one or more RF signalsand monitoring an amount of energy that is transferred via the one ormore RF signals from the at least one RF antenna to an RF receiver. Themethod additionally includes: adaptively adjusting a characteristic ofthe transmitter to optimize the amount of energy that is transferredfrom the at least one RF antenna to the RF receiver.

(A3) In accordance with some embodiments, a radio frequency (RF)charging pad is provided. The RF charging pad includes: one or moreprocessors for monitoring an amount of energy that is transferred fromthe RF charging pad to an RF receiver of an electronic device. The RFcharging pad also includes: one or more transmitting antenna elementsthat are configured to communicate with the one or more processors fortransmitting RF signals to the RF receiver of the electronic device. Insome embodiments, each respective antenna element includes: (i) aconductive line forming a meandered line pattern; (ii) an input terminalat a first end of the conductive line for receiving current that flowsthrough the conductive line at a frequency controlled by the one or moreprocessors; and (iii) a plurality of adaptive load terminals, distinctfrom the input terminal and distinct from each other, at a plurality ofpositions of the conductive line, each respective adaptive load terminalof the plurality of adaptive load terminals coupled with a respectivecomponent that is configured to be controlled by the one or moreprocessors and is configured to allow modifying a respective impedancevalue at the respective adaptive load terminal. In some embodiments, theone or more processors are configured to adaptively adjust at least oneof the frequency and a respective impedance value at one or more of theplurality of adaptive load terminals to optimize the amount of energythat is transferred from the one or more transmitting antenna elementsto the RF receiver of the electronic device.

(A4) In accordance with some embodiments, a method is also provided thatis used to charge an electronic device through radio frequency (RF)power transmission. The method includes: providing a charging pad thatincludes a transmitter comprising one or more RF antennas. In someembodiments, each RF antenna includes: (i) a conductive line forming ameandered line pattern; (ii) an input terminal at a first end of theconductive line for receiving current that flows through the conductiveline at a frequency controlled by one or more processors; and (iii) aplurality of adaptive load terminals, distinct from the input terminaland distinct from each other, at a plurality of positions of theconductive line, each respective adaptive load terminal of the pluralityof adaptive load terminals coupled with a respective component that iscontrolled by the one or more processors and allows for modifying arespective impedance value at the respective adaptive load terminal. Themethod also includes: transmitting, via the one or more RF antennas, oneor more RF signals, and monitoring an amount of energy that istransferred via the one or more RF signals from the one or more RFantennas to an RF receiver. The method additionally includes: adaptivelyadjusting a characteristic of the transmitter using the one or moreprocessors of the transmitter to optimize the amount of energy that istransferred from the one or more RF antennas to the RF receiver. In someembodiments, the characteristic is selected from a group consisting of(i) a frequency of the one or more RF signals, (ii) an impedance of thetransmitter, and (iii) a combination of (i) and (ii). In someembodiments, the impedance of the transmitter is adaptively adjusted ata respective one or more of the plurality of adaptive load terminals ofthe one or more RF antennas using the one or more processors of thetransmitter.

(A5) In accordance with some embodiments, a non-transitorycomputer-readable storage medium is provided. The non-transitorycomputer-readable storage medium includes executable instructions that,when executed by one or more processors that are coupled with a radiofrequency (RF) charging pad that includes one or more transmittingantenna elements, cause the one or more processors to: monitor an amountof energy that is transferred from the RF charging pad to an RF receiverof an electronic device; and communication with the one or moretransmitting antenna elements for transmitting RF signals to the RFreceiver of the electronic device. In some embodiments, each respectivetransmitting antenna element includes: a conductive line forming ameandered line pattern; an input terminal at a first end of theconductive line for receiving current that flows through the conductiveline at a frequency controlled by the one or more processors; and aplurality of adaptive load terminals, distinct from the input terminaland distinct from each other, at a plurality of positions of theconductive line, each respective adaptive load terminal of the pluralityof adaptive load terminals coupled with a respective component that isconfigured to be controlled by the one or more processors and isconfigured to allow modifying a respective impedance value at eachrespective adaptive load terminal. And the one or more processorsfurther adaptively adjust at least one of the frequency and a respectiveimpedance value at one or more of the plurality of adaptive loadterminals to optimize the amount of energy that is transferred from theone or more transmitting antenna elements to the RF receiver of theelectronic device.

(A6) In some embodiments of any of A1-A5, the frequency is in a firstfrequency band, and at least one of the one or more transmitting antennaelements is configured to operate at a second frequency band based onadaptive adjustments, by the one or more processors, to respectiveimpedance values at one or more of the plurality of adaptive loadterminals of the at least one transmitting antenna element.

(A7) In some embodiments of any of A1-A6, the RF charging pad includesan input circuit that is coupled with the one or more processors and isconfigured to provide the current to the input terminal at the first endof the conductive line, wherein the one or more processors areconfigured to adaptively adjust the frequency by instructing the inputcircuit to generate the current with a new frequency that is distinctfrom the frequency.

(A8) In some embodiments of any of A1-A7, the one or more processors areconfigured to adaptively adjust the frequency by instructing the feedingelement to generate the current with a plurality of differentfrequencies that are determined using predetermined increments.

(A9) In some embodiments of any of A1-A8, a respective conductive linefor at least one of the one or more transmitting antenna elements has arespective meandered line pattern that allows the at least onetransmitting antenna element to efficiently transmit RF signals havingthe frequency and/or the new frequency, at least two adjacent segmentsof the respective conductive line having the respective meandered linepattern have different geometric dimensions relative to each other, andthe respective conductive line has a length that remains the same whenthe at least one transmitting antenna element is configured to transmitRF signals having the frequency and/or the new frequency.

(A10) In some embodiments of any of A1-A9, at least one transmittingantenna element of the one or more transmitting antenna elements has afirst segment and a second segment, the first segment including theinput terminal, and the at least one transmitting antenna element isconfigured to: operate at the frequency while the first segment is notcoupled with the second segment, and operate at the new frequency whilethe first segment is coupled with the second segment; and the one ormore processors are configured to couple the first segment with thesecond segment in conjunction with instructing the feeding element togenerate the current with the new frequency that is distinct from thefrequency.

(A11) In some embodiments of any of A1-A10, the one or more processorsare configured to: adaptively adjust the frequency and/or a respectiveimpedance value associated with a first transmitting antenna element ofthe one or more transmitting antenna elements to cause the firsttransmitting antenna element to operate in a first frequency band, andadaptively adjust the frequency and/or the respective impedance valueassociated with a second transmitting antenna element of the one or moretransmitting antenna elements to cause the second transmitting antennaelement to operate in a second frequency band, wherein the firstfrequency band is distinct from the second frequency band.

(A12) In some embodiments of any of A1-A11, the electronic device isplaced in contact with or close to a top surface of the RF charging pad.

(A13) In some embodiments of any of A1-A12, the respective component isa mechanical relay coupled with the respective adaptive load terminalfor switching the respective adaptive load terminal between open andshort states, and the impedance value is adaptively adjusted at therespective adaptive load terminal of the respective transmitting antennaelement by opening or closing the mechanical relay to switch between anopen or short circuit, respectively.

(A14) In some embodiments of any of A1-A12, the respective component isan application-specific integrated circuit (ASIC), and the respectiveimpedance value is adaptively adjusted by the ASIC to within a range ofvalues.

(A15) In some embodiments of any of A1-A14, the one or more processorsare configured to: adaptively adjust the frequency and/or the respectiveimpedance value by adaptively adjusting the frequency and a respectiveimpedance value at one or more of the plurality of adaptive loadterminals to determine a relative maximum amount of energy that istransferred to the RF receiver of the electronic device, and once themaximum amount of energy is determined, cause each of the one or moretransmitting antenna elements to respectively transmit the RF signals ata respective frequency and using a respective impedance value thatresulted in the maximum amount of energy transferred to the RF receiver.

(A16) In some embodiments of any of A1-A15, the one or more processorsmonitor the amount of energy that is transferred to the RF receiverbased at least in part on information received from the electronicdevice, the information identifying energy received at the RF receiverfrom the RF signals.

(A17) In some embodiments of any of A1-A16, the information receivedfrom the electronic device identifying received energy is sent using awireless communication protocol.

(A18) In some embodiments of any of A1-A17, the wireless communicationprotocol is bluetooth low energy (BLE).

(A19) In some embodiments of any of A1-A18, the one or more processorsmonitor the amount of energy transferred based at least in part on anamount of energy that is detected at the respective adaptive loadterminal.

Thus, wireless charging systems configured in accordance with theprinciples described herein are able to charge an electronic device thatis placed at any position on the RF charging pad and avoid wastingenergy by ensuring that energy transfer is constantly optimized.

In addition, wireless charging systems configured in accordance with theprinciples described herein are able to charge different electronicdevices that are tuned at different frequencies or frequency bands onthe same charging transmitter. In some embodiments, a transmitter with asingle antenna element can operate at multiple frequencies or frequencybands at the same time or at different times. In some embodiments, atransmitter with multiple antenna elements can operate at multiplefrequencies or frequency bands at the same time. That enables moreflexibility in the types and sizes of antennas that are included inreceiving devices.

Note that the various embodiments described above can be combined withany other embodiments described herein. The features and advantagesdescribed in the specification are not all inclusive and, in particular,many additional features and advantages will be apparent to one ofordinary skill in the art in view of the drawings, specification, andclaims. Moreover, it should be noted that the language used in thespecification has been principally selected for readability andinstructional purposes, and not intended to circumscribe or limit theinventive subject matter.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the present disclosure can be understood in greater detail, amore particular description may be had by reference to the features ofvarious embodiments, some of which are illustrated in the appendeddrawings. The appended drawings, however, merely illustrate pertinentfeatures of the present disclosure and are therefore not to beconsidered limiting, for the description may admit to other effectivefeatures.

FIG. 1A is a high-level block diagram of an RF charging pad, inaccordance with some embodiments.

FIGS. 1B-1C are high-level block diagrams showing a portion of an RFcharging pad, in accordance with some embodiments.

FIG. 1D is a block diagram of a simplified circuit that illustratesenergy flow within sections of an antenna element that is transmittingan RF signal, in accordance with some embodiments.

FIG. 2 is a schematic of a transmitting antenna element with twoterminals, in accordance with some embodiments.

FIG. 3 is a flow chart of a method of charging an electronic devicethrough radio frequency (RF) power transmission.

FIGS. 4A-4E are schematics showing various configurations for individualantenna elements within an RF charging pad, in accordance with someembodiments.

FIGS. 5A-5D are schematics of an antenna element for an RF receiver, inaccordance with some embodiments.

FIG. 6 is a schematic of an RF charging pad with a plurality oftransmitting antenna elements (or unit cells), in accordance with someembodiments.

FIG. 7 is a schematic of a transmitting antenna element with a pluralityof adaptive loads of an RF charging pad, in accordance with someembodiments.

FIG. 8 is a flow chart of a method of charging an electronic devicethrough radio frequency (RF) power transmission by using at least one RFantenna with a plurality of adaptive loads, in accordance with someembodiments.

FIGS. 9A-9D are schematics showing various configurations for individualantenna elements that can operate at multiple frequencies or frequencybands within an RF charging pad, in accordance with some embodiments.

FIG. 10 is schematic showing an example configuration for an individualantenna element that can operate at multiple frequencies or frequencybands by adjusting the length of the antenna element, in accordance withsome embodiments.

In accordance with common practice, the various features illustrated inthe drawings may not be drawn to scale. Accordingly, the dimensions ofthe various features may be arbitrarily expanded or reduced for clarity.In addition, some of the drawings may not depict all of the componentsof a given system, method or device. Finally, like reference numeralsmay be used to denote like features throughout the specification andfigures.

DESCRIPTION OF EMBODIMENTS

Reference will now be made in detail to embodiments, examples of whichare illustrated in the accompanying drawings. In the following detaileddescription, numerous specific details are set forth in order to providea thorough understanding of the various described embodiments. However,it will be apparent to one of ordinary skill in the art that the variousdescribed embodiments may be practiced without these specific details.In other instances, well-known methods, procedures, components,circuits, and networks have not been described in detail so as not tounnecessarily obscure aspects of the embodiments.

FIG. 1A is a high-level block diagram of an RF charging pad, inaccordance with some embodiments. As shown in FIG. 1A, some embodimentsinclude a transmission pad 100 (also referred to herein as RF chargingpad 100 or RF transmission pad 100). In some embodiments, the RFcharging pad 100 includes one or more antenna elements that are eachpowered/fed by a respective power amplifier switch circuit 103 at afirst end and a respective adaptive load terminal 102 at a second end(additional details and descriptions of the one or more antenna elementsare provided below in reference to FIGS. 2A-2B).

In some embodiments, the RF charging pad 100 also includes (or is incommunication with) a central processing unit 110 (also referred to hereas processor 110). In some embodiments, the processor 110 is configuredto control RF signal frequencies and to control impedance values at eachof the adaptive load terminals 102 (e.g., by communicating with the loadpick or adaptive load 106, which may be an application-specificintegrated circuit (ASIC), or a variable resister, to generate variousimpedance values). In some embodiments, the load pick 106 is anelectromechanical switch that is placed in either an open or shortedstate.

In some embodiments, an electronic device (e.g., a device that includesa receiver 104 as an internally or externally connected component, suchas a remote that is placed on top of a charging pad 100 that may beintegrated within a housing of a streaming media device or a projector)and uses energy transferred from one or more RF antenna elements of thecharging pad 100 to the receiver 104 to charge a battery and/or todirectly power the electronic device.

In some embodiments, the RF charging pad 100 is configured with morethan one input terminal for receiving power (from power amplifier (PA)108, FIG. 1A) and more than one output or adaptive load terminal 102. Insome embodiments, the adaptive load terminals 102 at a particular zoneof the RF charging pad 100 (e.g., a zone that includes antenna elementslocated underneath a position at which an electronic device (with aninternally or externally connected RF receiver 104) to be charged isplaced on the charging pad) are optimized in order to maximize powerreceived by the receiver 104. For example, the CPU 110 upon receiving anindication that an electronic device with an internally or externallyconnected RF receiver 104 has been placed on the pad 100 in a particularzone 105 (the zone 105 includes a set of antenna elements) may adapt theset of antenna elements to maximize power transferred to the RF receiver104. Adapting the set of antenna elements may include the CPU 110commanding load pick 106 to try various impedance values for adaptiveload terminals 102 that are associated with the set of antenna elements.For example, the impedance value for a particular conductive line at anantenna element is given by the complex value of Z=A+jB (where A is thereal part of the impedance value and B is the imaginary part, e.g.,0+j0, 1000+j0, 0+50j, or 25+j75, etc.), and the load pick adjusts theimpedance value to maximize the amount of energy transferred from theset of antenna elements to the RF receiver 104. In some embodiments,adapting the set of antenna elements also or alternatively includes theCPU 110 causing the set of antenna elements to transmit RF signals atvarious frequencies until a frequency is found at which a maximum amountof energy is transferred to the RF receiver 104. In some embodiments,adjusting the impedance value and/or the frequencies at which the set ofantenna elements transmits causes changes to the amount of energytransferred to the RF receiver 104. In this way, the amount of energytransferred to the RF receiver 104 is maximized (e.g., to transfer atleast 75% of the energy transmitted by antenna elements of the pad 100to the receiver 104, and in some embodiments, adjusting the impedancevalue and/frequencies may allow up to 98% of the energy transmitted tobe received by the receiver 104) may be received at any particular pointon the pad 100 at which the RF receiver 104 might be placed.

In some embodiments, the input circuit that includes the power amplifier108 can additionally include a device that can change frequencies of theinput signal, or a device that can operate at multiple frequencies atthe same time, such as an oscillator or a frequency modulator.

In some embodiments, the CPU 110 determines that a maximum amount ofenergy is being transferred to the RF receiver 104 when the amount ofenergy transferred to the RF receiver 104 crosses a predeterminedthreshold (e.g., 75% or more of transmitted energy is received, such asup to 98%) or by testing transmissions with a number of impedance and/orfrequency values and then selecting the combination of impedance andfrequency that results in maximum energy being transferred to the RFreceiver 104 (as described in reference to the adaptation scheme below).

In some embodiments, an adaptation scheme is employed to adaptivelyadjust the impedance values and/or frequencies of the RF signal(s)emitted from the RF antenna(s) 120 of the charging pad 100, in order todetermine which combinations of frequency and impedance result inmaximum energy transfer to the RF receiver 104. For example, theprocessor 110 that is connected to the charging pad 100 tries differentfrequencies (i.e., in the allowed operating frequency range or ranges)at a given location of the RF charging pad 100 (e.g., a zone or area ofthe RF charging pad 100 that includes one or more RF antenna elementsfor transmitting RF signals, such as zone 105 of FIG. 1A) to attempt toadaptively optimize for better performance. For example, a simpleoptimization either opens/disconnects or closes/shorts each loadterminal to ground (in embodiments in which a relay is used to switchbetween these states), and may also cause RF antennas within the zone totransmit at various frequencies. In some embodiments, for eachcombination of relay state (open or shorted) and frequency, the energytransferred to the receiver 104 is monitored and compared to energytransferred when using other combinations. The combination that resultsin maximum energy transfer to the receiver 104 is selected and used tocontinue to transmitting the one or more RF signals to the receiver 104.

As another example, if five frequencies in the ISM band are utilized bythe pad 100 for transmitting radio frequency waves and the load pick 106is an electromechanical relay for switching between open and shortedstates, then employing the adaptation scheme would involve trying 10combinations of frequencies and impedance values for each antennaelement 120 or for a zone of antenna elements 120 and selecting thecombination that results in best performance (i.e., results in mostpower received at receiver 104, or most power transferred from the pad100 to the RF receiver 104).

The industrial, scientific, and medical radio bands (ISM bands) refersto a group of radio bands or parts of the radio spectrum that areinternationally reserved for the use of radio frequency (RF) energyintended for scientific, medical and industrial requirements rather thanfor communications. In some embodiments, all ISM bands (e.g., 40 MHz,900 MHz, 2.4 GHz, 5.8 GHz, 24 GHz, 60 GHz, 122 GHz, and 245 GHz) may beemployed as part of the adaptation scheme. As one specific example, ifthe charging pad 100 is operating in the 5.8 GHz band, then employingthe adaptation scheme would include transmitting RF signals and thenadjusting the frequency at predetermined increments (e.g., 50 MHzincrements, so frequencies of 5.75 GHz, 5.755 GHz, 5.76 GHz, and so on).In some embodiments, the predetermined increments may be 5, 10 15, 20,50 MHz increments, or any other suitable increment.

In some embodiments, the antenna elements 120 of the pad 100 may beconfigured to operate in two distinct frequency bands, e.g., a firstfrequency band with a center frequency of 915 MHz and a second frequencyband with a center frequency of 5.8 GHz. In these embodiments, employingthe adaptation scheme may include transmitting RF signals and thenadjusting the frequency at first predetermined increments until a firstthreshold value is reached for the first frequency band and thenadjusting the frequency at second predetermined increments (which may ormay not be the same as the first predetermined increments) until asecond threshold value is reached for the second frequency band. Forexample, the antenna elements 120 may be configured to transmit at 902MHz, 915 MHz, 928 MHZ (in the first frequency band) and then at 5.795GHz, 5.8 GHz, and 5.805 GHz (in the second frequency band). Additionaldetails regarding antenna elements that are capable of operating atmultiple frequencies are provided below in reference to FIGS. 9A-9D and10.

Turning now to FIGS. 1B-1C, high-level block diagrams showing a portionof an RF charging pad are illustrated, in accordance with someembodiments.

FIG. 1B shows a schematic of a single TX antenna 120 (which may be apart of an array of such antennas, all forming the charging pad 100 thatis shown in FIG. 1A). (In some embodiments, the TX antenna 120 is alsoreferred to as a TX antenna element 120). In some circumstances, an RFreceiving unit/antenna (RX) (or a device that includes the receivingunit 104 as an internally or externally connected component) is placedon top of a portion of the pad 100 that includes the TX antenna 120(which includes a conductive line that forms a meandered linearrangement, as shown in FIG. 1B).

In some embodiments, the receiver 104 has no direct contact to ametallic conductive line of the single TX antenna 120 and is justcoupled (i.e. in near-field zone) to the TX antenna 120.

In some embodiments, the TX antenna 120 has two or more terminals (orports) that are labeled as 121 (which may be a respective one of theterminals 102 of FIG. 1A) and 123 (which may be connected to arespective one of the PA switch circuits 103 of FIG. 1A) in FIG. 1B. Insome embodiments, the source of power (from the power amplifier or PA)is connected to terminal 123 and an adaptive load (e.g., anelectromechanical switch or ASIC) is connected to terminal 121. In someembodiments, the adaptive load is formed generally as a compleximpedance which may have both real and imaginary parts (i.e., a complexadaptive load can be formed using active devices (e.g., integratedcircuits or chips made of transistors) or passive devices formed byinductors/capacitors and resistors). In some embodiments, the compleximpedance is given by the formula Z=A+jB (e.g., 0+j0, 100+j0, 0+50j, andetc.), as discussed above.

In some embodiments, the receiver 104 may also be considered as a thirdterminal. To eliminate wasted energy, the receiver 104 should beconfigured to absorb a maximum amount (e.g., 75% or more, such as 98%)of the induced power that travels from terminal 123 and towards terminal121. In some embodiments, processor 110 is connected to the receiver 104through a feedback loop (e.g., by exchanging messages using ashort-range communication protocol, such by BLUETOOTH low energy (BLE)to exchange messages). In some alternative embodiments, the feedbackloop from the receiver back to the CPU at the transmitter may utilize asame frequency band as the power transmission signals transmitted by thepad 100, rather than using a separate communication protocol and/or adifferent frequency band.

In some embodiments, the feedback loop and messages exchanged may beused to indicate an amount of energy received or alternatively oradditionally may indicate an increase or decrease in the amount ofenergy received as compared to previous measurements. In someembodiments, the processor 110 monitors the amount of energy received bythe receiver 104 at certain points in time and controls/optimizes theadaptive load to maximize the power transferred from terminal 123 toterminal 121. In some embodiments, monitoring the amount of energytransferred includes one or both of (i) receiving information from thereceiver 104 (or a component of an electronic device in which thereceiver 104 is located) that indicates an amount of energy received bythe receiver 104 at a certain point in time and (ii) monitoring anamount of energy that remains in the conductive line at terminal 121(instead of having been absorbed by the receiver 104). In someembodiments, both of these monitoring techniques are utilized while, inother embodiments, one or the other of these monitoring techniques isutilized.

In some embodiments, the receiver 104 (i.e., an electronic device thatincludes the receiver 104 as an internally or externally connectedcomponent) may be placed anywhere on top of the charging pad 100 (i.e.,partially or fully covering the conductive line that forms a meanderedpattern on a respective antenna element 120) and the processor 110 willcontinue to monitor the amount of energy transferred and make neededadjustments (e.g., to impedance and/or frequency) to maximize the energytransferred to the receiver 104.

To help illustrate operation of the charging pad 100 and the antennaelements 120 included therein, the transmitting antenna element 120shown in FIG. 1B as divided into two sections: 1) section 125 starts atthe terminal 123 of the antenna element 120 and extends to an edge ofthe receiver 104; and 2) section 127 is formed by the rest of thetransmitting antenna element 120 and the terminal 121. The blocks aredescribed in more detail below with respect to FIG. 1C. It should beunderstood that sections 125 and 127 are functional representations usedfor illustrative purposes, and they are not intended to designate aspecific implementation that partitions an antenna element into separatesections.

Turning now to FIG. 1C, a block diagram of the TX antenna 120 is shown.In some embodiments, an effective impedance value (Z_(effective)),starting from a point that divides sections 125 and 127 and ending atthe TX antenna 120's connection to the adaptive load 106 (e.g., terminal121) will change based on location of the receiver 104 on the TX antenna120 and based on a selected load provided by adaptive load 106 at theterminal 121. In some embodiments, the selected load is optimized by theadaptive load 106 (in conjunction with the processor 110, FIG. 1A) totune Z_(effective) in such a way that the energy transferred betweenterminal 123 and the receiver 104 reaches a maximum (e.g., 75% or moreof energy transmitted by antenna elements of the pad 100 is received bythe RF receiver 104, such as 98%), while energy transfer may also stayat a minimum from terminal 123 to terminal 121 (e.g., less than 25% ofenergy transmitted by antenna elements of the pad 100 is not received bythe RF receiver 104 and ends up reaching terminal 121 or ends up beingreflected back, including as little as 2%).

In embodiments in which an electromechanical switch (e.g., a mechanicalrelay) is used to switch between open and shorted states, moving theswitch from the open to the shorted state (e.g., shorted to a groundplane) for a particular antenna element 120 causes the impedance value,Z_(effective), at a respective terminal 121 for that particular antennaelement 120 to drop to a value close to 0 (alternatively, switching fromthe shorted to the open state causes the impedance value to jump closeto a value close to infinity). In some embodiments, the frequencyadaptation scheme discussed above in reference to FIG. 1A is employed totest various combinations of impedance values and RF signal frequencies,in order to maximize energy transferred to an RF receiver (e.g.,receiver 104, FIGS. 1A-1C). In some embodiments, an integrated circuit(IC or chip) may be used instead of an electromechanical switch as theadaptive load 106. In such embodiments, the adaptive load 106 isconfigured to adjust the impedance value along a range of values, suchas between 0 and infinity. In some embodiments, the IC may be formed byadaptive/reconfigurable RF active and/or passive elements (e.g.,transistors and transmission lines) that are controlled by firmware ofthe IC (and/or firmware executing on the CPU 110 that controls operationof the IC). In some embodiments, the impedance produced by the IC, andcontrolled through firmware and based on information from the feedbackloop (discussed above in reference to FIG. 1A), may be changed to coverany load values selected from a Smith Chart (or the IC may be designedto produce certain loads covering a portion of values form the SmithChart). A Smith Chart may be sampled and stored in a memory (e.g., as alookup table) that is accessible by the processor 110, and the processor110 may perform lookups using the stored Smith Chart to determinevarious impedance values to test. For example, the integrated circuitmay be configured to select a predetermined number of complex values(e.g., 5j to 10j, 100+0j, or 0+50j, etc.) for the impedance value totest in combination with various RF transmission frequencies, in orderto locate a combination of values that optimizes energy transferred tothe receiver 104 (examples of maximized energy transfer are discussedabove).

In some other embodiments, a transmitter or charging pad with more thanone antenna elements 120 of FIG. 1B with one adaptive load 106 may beconfigured to operate in two or more distinct frequency bandsrespectively at the same time. For example, a first antenna elementoperates at a first frequency or frequency band, a second antennaelement operates at a second frequency or frequency band, and a thirdantenna element operates at a third frequency or frequency band, and afourth antenna element operates at a fourth frequency or frequency band,and the four frequency bands are distinct from each other. A transmitterwith two or more antenna elements 120 therefore can be used as amulti-band transmitter.

FIG. 1D is a block diagram of a simplified circuit that illustratesenergy flow within sections of an antenna element that is transmittingan RF signal, in accordance with some embodiments. The references topart1 and part2 in FIG. 1D refer to sections illustrated in FIGS. 1B and1C, in particular, part1 corresponds to section 125 and part2corresponds to section 127.

As shown in FIG. 1D, the effective impedance (Z_(effective)) for atransmitting antenna element 120 is formed by the portion of theconductive line that is after the receiver 104 (which, in someembodiments, forms a meandered line pattern as discussed in more detailbelow) and the adaptive load (labelled to as section 127 in FIGS. 1B and1C). In some embodiments, by optimizing, the load Z_(effective) will betuned so the energy transferred from PA to the receiver 104 ismaximized; and, the energy remaining in the conductive line by the timeit reaches the adaptive load is minimized (as discussed above).

FIG. 2 is a schematic of an antenna element with two terminals, inaccordance with some embodiments. As shown in FIG. 2, an input or firstterminal of the antenna element 120 (also described as terminal 123 inreference to FIGS. 1B-1D above) is connected with a power amplifier 108and an output or second terminal (also described as terminal 121 inreference to FIGS. 1B-1D above) is connected with a component 106 thatallows for configuring an adaptive load. Stated another way, in someembodiments, the antenna element 120 is fed by the power amplifier 108from the first terminal and the antenna element 120 is also terminatedat a second terminal at an adaptive load (for example, the mechanicalrelay that switches between shorted and open states).

In some embodiments, the charging pad 100 (FIG. 1A) is made ofsingle-layer or multi-layer copper antenna elements 120 with conductivelines that form a meandered line pattern. In some embodiments, each ofthese layers has a solid ground plane as one of its layers (e.g., abottom layer). One example of a solid ground plane is shown and labelledfor the transmitting antenna element shown in FIG. 2.

In some embodiments, the RF charging pad 100 (and individual antennaelements 120 included therein) is embedded in a consumer electronicdevice, such as a projector, a laptop, or a digital media player (suchas a networked streaming media player, e.g. a ROKU device, that isconnected to a television for viewing streaming television shows andother content). For example, by embedding the RF charging pad 100 in aconsumer electronic device, a user is able to simply place a peripheraldevice, such as a remote for a projector or a streaming media player(e.g., the remote for the projector or streaming media player includes arespective receiver 104, such as the example structures for a receiver104 shown in FIGS. 5A-5D), on top of the projector or the streamingmedia player and the charging pad 100 included therein will be able totransmit energy to a receiver 104 that is internally or externallyconnected to the remote, which energy is then harvested by the receiver104 for charging of the remote.

In some embodiments, the RF charging pad 100 may be included in a USBdongle as a standalone charging device on which a device to be chargedis placed. In some embodiments, the antenna elements 120 may be placednear a top surface, side surfaces, and/or a bottom surface of the USBdongle, so that a device to be charged may be placed at variouspositions that contact the USB dongle (e.g., a headphone that is beingcharged might sit on top of, underneath, or hang over the USB dongle andwould still be able to receive RF transmissions from the embedded RFcharging pad 100).

In some embodiments, the RF charging pad 100 is integrated intofurniture, such as desks, chairs, countertops, etc., thus allowing usersto easily charge their devices (e.g., devices that includes respectivereceivers 104 as internally or externally connected components) bysimply placing them on top of a surface that includes an integrated RFcharging pad 100.

Turning now to FIG. 3, a flow chart of a method 300 of charging anelectronic device through radio frequency (RF) power transmission isprovided. Initially, a transmitter is provided 302 that includes atleast one RF antenna (e.g., antenna element 120, FIGS. 1B-1D and 2) fortransmitting one or more RF signals or waves, i.e., an antenna designedto and capable of transmitting RF electromagnetic waves. In someembodiments, an array of RF antenna elements 120 are arranged adjacentto one another in a single plane, in a stack, or in a combination ofthereof, thus forming an RF charging pad 100. In some embodiments, theRF antenna elements 120 each include an antenna input terminal (e.g.,the first terminal 123 discussed above in reference to FIG. 2) and anantenna output terminal (e.g., the second terminal 121 discussed abovein reference to FIG. 2).

In some embodiments, a receiver (e.g., receiver 104, FIGS. 1A-1D) isalso provided 304. The receiver also includes one or more RF antennasfor receiving RF signals 310. In some embodiments, the receiver includesat least one rectenna that converts 318 the one or more RF signals intousable power to charge a device that includes the receiver 104 as aninternally or externally connected component. In use, the receiver 104is placed 306 within a near-field radio frequency distance to the atleast one antenna. For example, the receiver may be placed on top of theat least one RF antenna or on top of a surface that is adjacent to theat least one RF antenna, such as a surface of a charging pad 100.

One or more RF signals are then transmitted 308 via at the least one RFantenna. The system is then monitored 312/314 to determine the amount ofenergy that is transferred via the one or more RF signals from the atleast one antenna to a RF receiver (as is also discussed above). In someembodiments, this monitoring 312 occurs at the transmitter, while inother embodiments the monitoring 314 occurs at the receiver which sendsdata back to the transmitter via a back channel (e.g., over a wirelessdata connection using WIFI or BLUETOOTH). In some embodiments, thetransmitter and the receiver exchange messages via the back channel, andthese messages may indicate energy transmitted and/or received, in orderto inform the adjustments made at step 316.

In some embodiments, a characteristic of the transmitter is adaptivelyadjusted 316 to attempt to optimize the amount of energy that istransferred from the at least one RF antenna to the receiver. In someembodiments, this characteristic is a frequency of the one or more RFsignals and/or an impedance of the transmitter. In some embodiments, theimpedance of the transmitter is the impedance of the adjustable load.Also in some embodiments, the at least one processor is also configuredto control the impedance of the adaptive load. Additional details andexamples regarding impedance and frequency adjustments are providedabove.

In some embodiments, the transmitter includes a power input configuredto be electrically coupled to a power source, and at least one processor(e.g., processor 110, FIGS. 1A-1B) configured to control at least oneelectrical signal sent to the antenna. In some embodiments, the at leastone processor is also configured to control the frequency of the atleast one signal sent to the antenna.

In some embodiments, the transmitter further comprises a power amplifierelectrically coupled between the power input and the antenna inputterminal (e.g., PA 108, FIGS. 1A, 1C, 1D, and 2). Some embodiments alsoinclude an adaptive load electrically coupled to the antenna outputterminal (e.g., terminal 121, FIGS. 1A-1C and 2). In some embodiments,the at least one processor dynamically adjusts the impedance of theadaptive load based on the monitored amount of energy that istransferred from the at least one antenna to the RF receiver. In someembodiments, the at least one processor simultaneously controls thefrequency of the at least one signal sent to the antenna.

In some embodiments, each RF antenna of the transmitter includes: aconductive line forming a meandered line pattern, a first terminal(e.g., terminal 123) at a first end of the conductive line for receivingcurrent that flows through the conductive line at a frequency controlledby one or more processors, and a second terminal (e.g., terminal 121),distinct from the first terminal, at a second end of the conductiveline, the second terminal coupled to a component (e.g., adaptive load106) controlled by the one or more processors and that allows formodifying an impedance value of the conductive line. In someembodiments, the conductive line is disposed on or within a firstantenna layer of a multi-layered substrate. Also in some embodiments, asecond antenna is disposed on or within a second antenna layer of themulti-layered substrate. Finally, some embodiments also provide a groundplane disposed on or within a ground plane layer of the multi-layeredsubstrate.

FIGS. 4A-4E are schematics showing various configurations for individualantenna elements within an RF charging pad, in accordance with someembodiments. As shown in FIGS. 4A-4E, an RF charging pad 100 (FIG. 1A)may include antenna elements 120 that are made using differentstructures.

For example, FIGS. 4A-4B show examples of structures for an antennaelement 120 that includes multiple layers that each include conductivelines formed into meandered line patterns. The conductive lines at eachrespective layer may have the same (FIG. 4B) or different (FIG. 4A)widths (or lengths, or trace gauges, or patterns, spaces between eachtrace, etc.) relative to other conductive lines within a multi-layerantenna element 120. In some embodiments, the meandered line patternsmay be designed with variable lengths and/or widths at differentlocations of the pad 100 (or an individual antenna element 120), and themeandered line patterns may be printed on more than one substrate of anindividual antenna element 120 or of the pad 100. These configurationsof meandered line patterns allow for more degrees of freedom and,therefore, more complex antenna structures may be built that allow forwider operating bandwidths and/or coupling ranges of individual antennaelements 120 and the RF charging pad 100.

Additional example structures are provided in FIGS. 4C-4E: FIG. 4C showsan example of a structure for an antenna element 120 that includesmultiple layers of conductive lines forming meandered line patterns thatalso have sliding coverage (in some embodiments, respective meanderedline patterns may be placed in different substrates with just a portionof a first meandered line pattern of a respective substrate overlappingthe a second meandered line pattern of a different substrate (i.e.,sliding coverage), and this configuration helps to extend coveragethroughout width of the antenna structure); FIG. 4D shows an example ofa structure for an antenna element 120 that includes a conductive linehaving different lengths at each turn within the meandered line pattern(in some embodiments, using different lengths at each turn helps toextend coupling range of the antenna element 120 and/or helps add to theoperating bandwidth of the RF charging pad 100); and FIG. 4E shows anexample of a structure for an antenna element 120 that includes aconductive line that forms two adjacent meandered line patterns (in someembodiments, having a conductive line that forms two adjacent meanderedline patterns helps to extend width of the antenna element 120). All ofthese examples are non-limiting and any number of combinations andmulti-layered structures are possible using the example structuresdescribed above.

FIGS. 5A-5D are schematics of an antenna element for an RF receiver, inaccordance with some embodiments. In particular FIGS. 5A-5D showexamples of structures for RF receivers (e.g., receiver 104, FIGS. 1A-1Dand 2), including: (i) a receiver with a conductive line that formsmeandered line patterns (the conductive line may or may not be backed bysolid ground plane or reflector), as shown in FIGS. 5A (single-polarityreceiver) and 5B (dual-polarity receiver). FIGS. 5C-5D show additionalexamples of structures for an RF receiver with dual-polarity and aconductive line that forms a meandered line pattern. Each of thestructures shown in FIGS. 5A-5D may be used to provide differentcoupling ranges, coupling orientations, and/or bandwidth for arespective RF receiver. As a non-limiting example, when the antennaelement shown in FIG. 5A is used in a receiver, very small receivers maybe designed/built that only couple to the pad 100 in one direction. Asanother non-limiting example, when the antenna elements shown in FIGS.5B-5D are used in a receiver, the receiver is then able to couple to thepad 100 in any orientation.

Commonly-owned U.S. patent application Ser. No. 15/29,729 also providesadditional examples and descriptions of meandered line patterns forantenna elements (e.g., those shown in FIGS. 2A-2D, 3, 4, 5, 7, 8, and9A-9B, and described in the specification) and descriptions of thefunctioning of power transfer systems that include antenna elements withmeandered line patterns (e.g., paragraphs [0022]-[0034] and FIGS.1A-1B), and the disclosure of this commonly-owned application thussupplements the descriptions of antenna elements with meandered linepatterns provided herein (for both receivers and transmitters, or acombination thereof).

FIG. 6 is a schematic of an RF charging pad with a plurality oftransmitting antenna elements (unit cells) that form a larger RFcharging/transmitting pad, in accordance with some embodiments. In someembodiments, the RF charging pad 100 is formed as an array of adjacentantenna elements 120 (the distance between cells may be optimized forthe best coverage). In some embodiments, when a receiver is placed in anarea/gap that is between adjacent antenna elements 120, attempts tooptimize energy transfer (e.g., in accordance with the adaptation schemediscussed above in reference to FIG. 1A) may not result in increasedenergy transfer above an acceptable threshold level (e.g., 75% or more).As such, in these circumstances, adjacent antenna elements may both beconfigured to transmit RF waves at full power at the same time totransfer additional energy to a receiver that is placed on a surface ofthe RF charging pad, and at a location that is between adjacent antennaelements 120.

As one possible configuration in accordance with some embodiments, port(or terminal) group #1 (FIG. 6) supplies power, port (or terminal)groups #2 and #3 provide adaptive loads (e.g., an electromechanicalrelay moving between short-circuit and open-circuit states). As anotherexample of a suitable configuration, port (or terminal) groups #1, #2and #3 may also be used to supply power via a power amplifier to thecharging pad 100 (at the same time or with one group at a time beingswitched when necessary).

In some embodiments, each transmitting antenna element 120 of the RFcharging pad 100 forms a separate coupling zone which is controlled by afeeding (PA) terminal and one or more terminals to support adaptiveload(s), as explained in detail above. In some embodiments, feedbackfrom the receiver helps determine the zone on top of which the receiveris placed, and this determination activates that zone. In circumstancesin which the receiver is placed between two or more zones (e.g., at anarea/gap that is between adjacent antenna elements 120), additionaladjacent zones might be activated to ensure sufficient transfer ofenergy to the receiver.

The antenna elements 120 described above (e.g., in reference to FIG. 1B)may also be configured to have multiple adaptive load terminals (e.g.,multiple adaptive load terminals 121) that are coupled to at differentpositions along a respective antenna element 120. An example of anantenna element 120 with multiple adaptive load terminals is providedbelow in reference to FIG. 7. FIG. 7 is a schematic showing atransmitting antenna element (unit cell) with a plurality of adaptiveloads (which may be a part of an array of such antennas, as describedabove in reference to FIGS. 1-6) of an RF charging pad, in accordancewith some embodiments. In some embodiments, the RF charging pad 700includes one or more antenna elements 701 (which may be any of theantenna elements as shown in FIGS. 1B, 2, 4A-4E, 5A-5D, and 6). Eachantenna element 701 is powered/fed by a respective power amplifier (PA)switch circuit 708 (which may be a respective one of the PA switchcircuits 103 of FIG. 1A) that may be connected to a respective poweramplifier 708 or a source of power at a first end of the antenna element701.

In some embodiments, the input circuit that includes the power amplifier708 may additionally include a device that can change frequencies of theinput signal or a device that can operate at multiple frequencies at thesame time, such as an oscillator or a frequency modulator.

In some embodiments, each antenna element 701 of the RF charging pad 700includes a plurality of respective adaptive load terminals 702, forexample, 702 a, 702 b, 702 c, . . . 702 n, at a plurality of positionswithin a respective antenna element 701. In some embodiments, theantenna element 701 includes a conductive line forming a meandered linepattern (as discussed above in reference to FIGS. 1, 2, and 4-6). Insome embodiments, each adaptive load terminals of the plurality ofadaptive load terminals 702 for the antenna element 701 is located atdifferent positions on the conductive meandered line of the antennaelement 701 as shown in FIG. 7.

In some embodiments, a meandered line antenna element 701 includes aconductive line with multiple turns in one plane. In some embodiments,the multiple turns may be square turns as shown for the antenna element701 in FIG. 7. In some embodiments, the multiple turns may beround-edged turns. The conductive line may also have segments of varyingwidths, for example, a segment 706 having a first width, andshort-length segment 707 that has a second width that is less than thefirst width. In some embodiments, at least one of the adaptive loadterminals 702 a is positioned at one of the short-length segments (e.g.,short-length segment 707) and another adaptive load terminal ispositioned anywhere at one of the segments 706 having the first width.In some embodiments, at least one of the adaptive load terminals 702 ispositioned or connected anywhere on a width segment, for example, at themiddle of a width segment of the meandered line antenna element 701. Insome embodiments, the last adaptive load terminal 702 n is positioned ata second end of the conductive line (opposite to a first end at theinput terminal 703 of the antenna element 701 described above inreference to FIGS. 1, 2, and 4-6). In some embodiments, in certaindesign and optimization, an adaptive load terminal is not necessarilypositioned at a second end of the meandered line antenna element 701 butcan be positioned at any location of the antenna element 701.

In some embodiments, the RF charging pad 700 also includes (or is incommunication with) a central processing unit 710 (also referred to hereas processor 710). In some embodiments, the processor 710 is configuredto control RF signal frequencies and to control impedance values at eachof the adaptive load terminals 702, e.g., by communicating with aplurality of the load picks or adaptive loads 712, for example, 712 a,712 b, 712 c, . . . 712 n, for each of the adaptive load terminals 702(as discussed above in reference to load pick or adaptive load 106 inFIGS. 1A and 1B).

In some embodiments, an electronic device (e.g., a device that includesa receiver 704 as an internally or externally connected component, suchas a remote that is placed on top of a charging pad 700 that may beintegrated within a housing of a streaming media device or a projector)and uses energy transferred from one or more RF antenna elements 701 ofthe charging pad 700 to the receiver 704 to charge a battery and/or todirectly power the electronic device.

In some embodiments, the adaptive load terminals 702 at a particularzone or selected positions of the antenna element 701 (e.g., a zone onthe antenna element 701 located underneath a position at which anelectronic device (with an internally or externally connected RFreceiver 704) to be charged is placed on the charging pad) are optimizedin order to maximize power received by the receiver 704. For example,the CPU 710 upon receiving an indication that an electronic device withan internally or externally connected RF receiver 704 has been placed onthe pad 700 in a particular zone on the antenna element 701 may adaptthe plurality of adaptive loads 712, for example, adaptive loads 712 a,712 b, 712 c, . . . 712 n, that are respectively coupled to the adaptiveterminals 702, in order to maximize power transferred to the RF receiver704. Adapting the set of adaptive loads 712 may include the CPU 710commanding one or more of the adaptive loads to try various impedancevalues for one or more of the adaptive load terminals 702 that arecoupled to different positions of the antenna element 701. Additionaldetails regarding adapting adaptive loads were provided above, and, forthe sake of brevity, are not repeated here.

The effective impedance value (Z_(effective)) at a particularposition/portion of the conductive line of the antenna element 701 isaffected by a number of variables and may be manipulated by adjustingconfigurations of the adaptive load terminals 712 that are coupled tovarious positions on the antenna element 701. In some embodiments, aneffective impedance value (Z_(effective)), starting from a point thatdivides sections 725 (which starts at the terminal 703 of the antennaelement 701 and extends to an edge of the receiver 704) and 727 (whichis formed by the rest of the transmitting antenna element 701 and theterminal 702 n) and ending at the TX antenna 701's connection to theadaptive load 712 n (e.g., terminal 702 n) will change based on locationof the receiver 704 on the TX antenna 701 and based on a set of selectedloads provided by adaptive loads 712 at various positions within section727. In some embodiments, the selected loads are optimized by theadaptive loads 712 (in conjunction with the processor 710) to tuneZ_(effective) in such a way that the energy transferred between terminal703 and the receiver 704 reaches a maximum (e.g., 75% or more of energytransmitted by antenna elements of the pad 700 is received by the RFreceiver 704, such as 98%), while energy transfer may also stay at aminimum from terminal 703 to terminal 702 n (e.g., less than 25% ofenergy transmitted by antenna elements of the pad 700 is not received bythe RF receiver 704 and ends up reaching terminals positioned withinsection 727 or ends up being reflected back, including as little as 2%).

In some embodiments, a selected several adaptive loads 712 of theplurality of adaptive loads 712 are used (by the processor 710) on theantenna element 701 to adjust the impedance and/or frequency of theantenna element 701. In one example, with reference to FIG. 7, onlyadaptive load terminals 702 a and 702 c are connected at a particularpoint in time to adaptive loads 712 a and 712 c respectively, whileadaptive load terminals 702 b and 702 n are disconnected at theparticular point in time. In another example, with reference to FIG. 7,only adaptive load terminals 702 a and 702 n are connected at aparticular point in time to adaptive loads 712 a and 712 n,respectively, while adaptive load terminals 702 b and 702 c aredisconnected at the particular point in time. In some embodiments, allof the adaptive load terminals 702 are connected at a particular pointin time to their respective adaptive loads 712. In some embodiments,none of the adaptive load terminals 702 are connected at a particularpoint in time to their respective adaptive loads 712. In someembodiments, the impedance value of each of the adaptive loads 712connected to a selected adaptive load terminal 712 is adjustedindividually to optimize the energy transfer.

In embodiments in which a meandered line antenna has been optimized forthe multi-band operation, the multiple adaptive load configurationwithin a single antenna element also enables a broader frequency bandadjustment compared with a single adaptive load configuration within asingle antenna element as described in FIG. 1B above. The multipleadaptive load configuration within a single antenna element furtherenhances multiple frequency band operation on a single antenna element.For example, a single antenna element 701 with multiple adaptive loadterminals is capable of operating at a wider frequency band than acorresponding antenna element that is configured with one adaptive loadterminal.

In some embodiments, adapting the set of adaptive loads 712 also oralternatively includes the CPU 710 causing the set of antenna elementsto transmit RF signals at various frequencies until a frequency is foundat which a maximum amount of energy is transferred to the RF receiver704. In some embodiments, for example, one of the antenna elementstransmits RF signals at a first frequency, and another one of theantenna elements transmits RF signals at a second frequency that isdifferent from the first frequency. In some embodiments, adjusting theimpedance value and/or the frequencies at which the set of antennaelements transmits causes changes to the amount of energy transferred tothe RF receiver 704. In this way, the amount of energy transferred tothe RF receiver 704 that is maximized (e.g., to transfer at least 75% ofthe energy transmitted by antenna elements of the pad 700 to thereceiver 704, and in some embodiments, adjusting the impedance valueand/frequencies may allow up to 98% of the energy transmitted to bereceived by the receiver 704) may be received at any particular point onthe pad 700 at which the RF receiver 704 might be placed.

In some embodiments, the CPU 710 determines that a maximum amount ofenergy is being transferred to the RF receiver 704 when the amount ofenergy transferred to the RF receiver 704 crosses a predeterminedthreshold (e.g., 75% or more of transmitted energy is received, such asup to 98%) or by testing transmissions with a number of impedance and/orfrequency values and then selecting the combination of impedance andfrequency that results in maximum energy being transferred to the RFreceiver 704 (also as described in reference to the adaptation scheme inFIGS. 1A-1D above). In some embodiments, processor 710 is connected tothe receiver 704 through a feedback loop (e.g. by exchanging messagesusing a wireless communication protocol, such as BLUETOOTH low energy(BLE), WIFI, ZIGBEE, infrared beam, near-field transmission, etc, toexchange messages). In some embodiments, the adaptation scheme isemployed to test various combinations of impedance values of theadaptive impedance loads 712 and RF frequencies, in order to maximizeenergy transferred to an RF receiver 704. In such embodiments, each ofthe adaptive load 712 is configured to adjust the impedance value alonga range of values, such as between 0 and infinity. In some embodiments,the adaptation scheme is employed when one or more RF receivers areplaced on top of one of the antenna element 701.

In some embodiments, an adaptation scheme is employed to adaptivelyadjust the impedance values and/or frequencies of the RF signal(s)emitted from the RF antenna(s) 701 of the charging pad 700, in order todetermine which combinations of frequency and impedance result inmaximum energy transfer to the RF receiver 704. For example, theprocessor 710 that is connected to the charging pad 700 tries differentfrequencies (i.e., in the allowed operating frequency range or ranges)by using different selected sets of adaptive loads 712 at differentlocations of the antenna element 701, e.g. enabling or disabling certainadaptive loads 712, to attempt to adaptively optimize for betterperformance. For example, a simple optimization either opens/disconnectsor closes/shorts each load terminal to ground (in embodiments in which arelay is used to switch between these states), and may also cause RFantenna element 701 to transmit at various frequencies. In someembodiments, for each combination of relay state (open or shorted) andfrequency, the energy transferred to the receiver 704 is monitored andcompared to energy transferred when using other combinations. Thecombination that results in maximum energy transfer to the receiver 704is selected and used to continue to transmitting the one or more RFsignals using one or more antenna elements 701 to the receiver 704.

In some embodiments, the single antenna element 701 with multipleadaptive loads 712 of the pad 700 may be configured to operate in two ormore distinct frequency bands (such as the ISM bands described above),e.g., a first frequency band with a center frequency of 915 MHz and asecond frequency band with a center frequency of 5.8 GHz. In theseembodiments, employing the adaptation scheme may include transmitting RFsignals and then adjusting the frequency at first predeterminedincrements until a first threshold value is reached for the firstfrequency band and then adjusting the frequency at second predeterminedincrements (which may or may not be the same as the first predeterminedincrements) until a second threshold value is reached for the secondfrequency band. In some embodiments, a single antenna element canoperate at multiple different frequencies within one or more frequencybands. For example, the single antenna element 701 may be configured totransmit at 902 MHz, 915 MHz, 928 MHZ (in the first frequency band) andthen at 5.795 GHz, 5.8 GHz, and 5.805 GHz (in the second frequencyband). The single antenna element 701 can operate at more than onefrequency bands as a multi-band antenna. A transmitter with at least oneantenna element 701 can be used as a multi-band transmitter.

In some embodiments, multiple antenna elements 701 each with multipleadaptive loads 712 may be configured within a particular transmissionpad to allow the particular transmission pad to operate in two or moredistinct frequency bands respectively at the same time. For example, afirst antenna element 701 of the particular transmission pad operates ata first frequency or frequency band, a second antenna element 701 of theparticular transmission pad operates at a second frequency or frequencyband, and a third antenna element 701 of the particular transmission padoperates at a third frequency or frequency band, and a fourth antennaelement 701 of the particular transmission pad operates at a fourthfrequency or frequency band, and the four frequency bands are distinctfrom each other. In this way, the particular transmission pad isconfigured to operate at multiple different frequency bands.

In some embodiments, the transmitter described herein can transmitwireless power in one frequency or frequency band, and transmit andexchange data with a receiver in another frequency or frequency band.

Different antenna elements operating at different frequencies canmaximize energy transfer efficiency when a smaller device is chargedwith higher frequencies and a larger device is charged with lowerfrequencies on the same charging pad. For example, devices that requirea higher amount of power, such as mobile phones, may also have morespace to include larger antennas, thus making a lower frequency of 900MHz a suitable frequency band. As a comparison, a smaller device, suchas an earbud, may require a small amount of power and may also have lessspace available for longer antennas, thus making a higher frequency of2.4 or 5.8 GHz a suitable frequency band. This configuration enablesmore flexibility in the types and sizes of antennas that are included inreceiving devices.

Turning now to FIG. 8, in accordance with some embodiments, a flow chartof a method 800 of charging an electronic device through radio frequency(RF) power transmission by using at least one RF antenna with aplurality of adaptive loads is provided. Initially, a charging padincluding a transmitter is provided in step 802 that includes at leastone RF antenna (e.g., antenna element 701, as described with respect toFIG. 7 above which further includes FIGS. 1-6) for transmitting one ormore RF signals or waves, i.e., an antenna designed to and capable oftransmitting RF electromagnetic waves. In some embodiments, an array ofRF antenna elements 701 are arranged adjacent to one another in a singleplane, in a stack, or in a combination of thereof, thus forming an RFcharging pad 700 (as described in reference to FIGS. 4A-4E, 5A-5D and6). In some embodiments, the RF antenna elements 701 each include anantenna input terminal (e.g., the first terminal 703 discussed above inreference to FIG. 7) and a plurality of antenna output terminals (e.g.,the plurality of adaptive load terminals 702 discussed above inreference to FIG. 7). In some embodiments, the antenna element 701includes a conductive line that forms a meandered line arrangement (asshown in FIGS. 1-2, and 4-7). The plurality of adaptive load terminals702 are positioned at different locations of the conductive line of theantenna element 701.

In some embodiments, the transmitter further comprises a power amplifierelectrically coupled between the power input and the antenna inputterminal (e.g., PA 708 in FIG. 7). Some embodiments also includerespective adaptive loads 712 a, 712 b, 712 c, . . . 712 n electricallycoupled to the plurality of antenna output terminals (e.g., adaptiveload terminals 702 in FIG. 7). In some embodiments, the transmitterincludes a power input configured to be electrically coupled to a powersource, and at least one processor (e.g., processor 710 in FIG. 7, andprocessor 110 in FIGS. 1A-1B) configured to control at least oneelectrical signal sent to the antenna. In some embodiments, the at leastone processor is also configured to control the frequency and/oramplitude of the at least one signal sent to the antenna.

In some embodiments, each RF antenna of the transmitter includes: aconductive line forming a meandered line pattern, a first terminal(e.g., terminal 703) at a first end of the conductive line for receivingcurrent that flows through the conductive line at a frequency controlledby one or more processors, and a plurality of adaptive load terminals(e.g., terminals 702), distinct from the first terminal, at a pluralityof positions of the conductive line, the plurality of adaptive loadterminals coupled to a respective component (e.g., adaptive loads 712 inFIG. 7) controlled by the one or more processors and that allows formodifying an impedance value of the conductive line. In someembodiments, the conductive line is disposed on or within a firstantenna layer of a multi-layered substrate. Also in some embodiments, asecond antenna is disposed on or within a second antenna layer of themulti-layered substrate. Finally, some embodiments also provide a groundplane disposed on or within a ground plane layer of the multi-layeredsubstrate.

In some embodiments, a receiver (e.g., receiver 704 in reference to FIG.7) is also provided (also as described in reference to FIG. 3). Thereceiver also includes one or more RF antennas for receiving RF signals.In some embodiments, the receiver includes at least one rectenna thatconverts the one or more RF signals into usable power to charge a devicethat includes the receiver 704 as an internally or externally connectedcomponent (see also steps 304, 306, 310, 314 and 318 in reference toFIG. 3). In use, the receiver 704 is placed within a near-field radiofrequency distance to the at least one antenna of the transmitter or thecharging pad. For example, the receiver may be placed on top of the atleast one RF antenna 701 or on top of a surface that is adjacent to theat least one RF antenna 701, such as a surface of a charging pad 700.

In step 804, one or more RF signals are then transmitted via at theleast one RF antenna 701.

The system is then monitored in step 806 to determine the amount ofenergy that is transferred via the one or more RF signals from the atleast one antenna 701 to one or more RF receivers (as is also discussedabove). In some embodiments, this monitoring 806 occurs at thetransmitter, while in other embodiments the monitoring 806 occurs at thereceiver which sends data back to the transmitter via a back channel(e.g., over a wireless data connection using WIFI or BLUETOOTH). In someembodiments, the transmitter and the receiver exchange messages via theback channel, and these messages may indicate energy transmitted and/orreceived, in order to inform the adjustments made at step 808.

In some embodiments, in step 808, a characteristic of the transmitter isadaptively adjusted to attempt to optimize the amount of energy that istransferred from the at least one RF antenna 701 to the receiver. Insome embodiments, this characteristic is a frequency of the one or moreRF signals and/or an impedance of the transmitter. In some embodiments,the impedance of the transmitter is the impedance of the adjustableloads. Also in some embodiments, the at least one processor is alsoconfigured to control the impedance of the selected set of the pluralityof adaptive loads 712. Additional details and examples regardingimpedance and frequency adjustments are provided above.

In some embodiments, the at least one processor (e.g. CPU 710 in FIG. 7)dynamically adjusts the impedance of the adaptive load based on themonitored amount of energy that is transferred from the at least oneantenna 701 to the RF receiver. In some embodiments, the at least oneprocessor simultaneously controls the frequency of the at least onesignal sent to the antenna.

In some embodiments, the single antenna element 701 with multipleadaptive loads 712 of the pad 700 may be dynamically adjusted by the oneor more processors to operate in two or more distinct frequency bands(such as the ISM bands described above) at the same time or at differenttimes, e.g., a first frequency band with a center frequency of 915 MHzand a second frequency band with a center frequency of 5.8 GHz. In theseembodiments, employing the adaptation scheme may include transmitting RFsignals and then adjusting the frequency at first predeterminedincrements until a first threshold value is reached for the firstfrequency band and then adjusting the frequency at second predeterminedincrements (which may or may not be the same as the first predeterminedincrements) until a second threshold value is reached for the secondfrequency band. For example, the single antenna element 701 may beconfigured to transmit at 902 MHz, 915 MHz, 928 MHZ (in the firstfrequency band) and then at 5.795 GHz, 5.8 GHz, and 5.805 GHz (in thesecond frequency band). The single antenna element 701 can operate atmore than one frequency bands as a multi-band antenna. A transmitterwith at least one antenna element 701 can be used as a multi-bandtransmitter.

In some embodiments, a charging pad or transmitter may include one ormore of the antenna element 701 with a plurality of adaptive loads asdescribed in FIG. 7 and one or more antenna element 120 with oneadaptive load as described in FIG. 1A-1D.

FIGS. 9A-9D are schematics showing various configurations for individualantenna elements that can operate at multiple frequencies or frequencybands within an RF charging pad, in accordance with some embodiments. Asshown in FIGS. 9A-9D, an RF charging pad 100 (FIGS. 1A-1B) or an RFcharging pad 700 (FIG. 7) may include antenna elements 120 (FIG. 1B) or701 (FIG. 7) that configured to have conductive line elements that havevarying physical dimensions.

For example, FIGS. 9A-9D show examples of structures for an antennaelement that each include a conductive line formed into differentmeandered line patterns at different portions of the element. Theconductive lines at different portions or positions of the element mayhave different geometric dimensions (such as widths, or lengths, ortrace gauges, or patterns, spaces between each trace, etc.) relative toother conductive lines within an antenna element. In some embodiments,the meandered line patterns may be designed with variable lengths and/orwidths at different locations of the pad (or an individual antennaelement). These configurations of meandered line patterns allow for moredegrees of freedom and, therefore, more complex antenna structures maybe built that allow for wider operating bandwidths and/or couplingranges of individual antenna elements and the RF charging pad.

In some embodiments, the antennas elements 120 and 701 described hereinmay have any of the shapes illustrated in FIGS. 9A-9D. In someembodiments, each of the antenna elements shown in FIGS. 9A-9D has aninput terminal (123 in FIG. 1B or 703 in FIG. 7) at one end of theconductive line and at least one adaptive load terminals (121 in FIG. 1Bor 702 a-n in FIG. 7) with adaptive loads (106 in FIG. 1B or 712 a-n inFIG. 7) as described above at another end or a plurality of positions ofthe conductive line.

In some embodiments, each of the antenna elements shown in FIGS. 9A-9Dcan operate at two or more different frequencies or two or moredifferent frequency bands. For example, a single antenna element canoperate at a first frequency band with a center frequency of 915 MHz ata first point in time and a second frequency band with a centerfrequency of 5.8 GHz at a second point in time, depending on whichfrequency is provided at an input terminal of each of the antennaelements. Moreover, the shapes of the meandered line patterns shown inFIGS. 9A-9D are optimized to allow the antenna elements to operateefficiently at multiple different frequencies.

In some embodiments, each of the antenna elements shown in FIGS. 9A-9Dcan operate at two or more different frequencies or two or moredifferent frequency bands at the same time when the input terminal issupplied with more than two distinct frequencies that can besuperimposed. For example, a single antenna element can operate at afirst frequency band with a center frequency of 915 MHz and a secondfrequency band with a center frequency of 5.8 GHz at the same time whenboth frequency bands with a first center frequency of 915 MHz and asecond center frequency of 5.8 GHz are supplied at the input terminal ofthe conductive line. In yet another example, a single antenna elementcan operate at multiple different frequencies within one or morefrequency bands.

In some embodiments, the operating frequencies of the antenna elementscan be adaptively adjusted by one or more processors (110 in FIGS. 1A-1Bor 710 in FIG. 7) as described above according to the receiver antennadimension, frequency, or the receiver loads and the adaptive loads onthe charging pad.

In some embodiments, each of the antenna elements shown in FIGS. 9A-9Dwith different meandered patterns at different portions of theconductive line can operate more efficiently at multiple frequenciescompared with the more symmetrical meandered line structures (Forexample, FIG. 1B, 2, 4A-4B, or 6). For example, energy transferefficiency at different operating frequencies of the antenna elementsshown in FIGS. 9A-9D with different meandered patterns at differentportions of the conductive line can be improved by about at least 5%,and in some instance at least 60%, more than the more symmetricalmeandered line structure elements. For example, the more symmetricalmeandered line structure antenna element may be able to transfer no morethan 60% of transmitted energy to a receiving device while operating ata new frequency other than a frequency for which the more symmetricalmeandered line structure antenna element has been designed (e.g., if themore symmetrical meandered line structure antenna element is designed tooperate at 900 MHz, if it then transmits a signal having a frequency of5.8 GHz it may only be able to achieve an energy transfer efficiency of60%). In contrast, the antenna element with different meandered patterns(e.g., those shown in FIGS. 9A-9D) may be able to achieve an energytransfer efficiency of 80% or more while operating at variousfrequencies. In this way, the designs for antenna elements shown inFIGS. 9A-9D ensure that a single antenna element is able to achieve amore efficient operation at various different frequencies.

FIG. 10 is schematic showing an example configuration for an individualantenna element that can operate at multiple frequencies or frequencybands by adjusting the length of the antenna element, in accordance withsome embodiments.

In some embodiments as shown in FIG. 10, at least one transmittingantenna element 1002 (as described in FIGS. 1-9) of the one or moretransmitting antenna elements of an RF charging pad 1000 has a firstconductive segment 1004 (a first portion of a meandered conductive line,such as any of those described above for antenna elements 120 and 701)and a second conductive segment 1006 (a second portion of the meanderedconductive line, such as any of those described above for antennaelements 120 and 701). In some embodiments, the first conductive segmentincludes an input terminal (123 in FIG. 1B or 703 in FIG. 7). In someembodiments, the at least one transmitting antenna element 1002 isconfigured to operate at a first frequency (e.g., 2.4 GHz) while thefirst conductive segment 1004 is not coupled with the second conductivesegment 1006. In some embodiments, the at least one transmitting antennaelement 1002 is configured to operate at a second frequency (e.g., 900MHz) which is different from the first frequency while the firstconductive segment is coupled with the second conductive segment.

In some embodiments, one or more processors (110 in FIGS. 1A-1B or 710in FIG. 7) are configured to cause coupling of the first segment withthe second segment in conjunction with instructing a feeding element (asdescribed as 108 in FIGS. 1A-1B and 708 in FIG. 7) to generate currentwith a second frequency (e.g., 900 MHz) that is distinct from the firstfrequency (e.g., 2.4 GHz), thereby allowing the antenna element 1002 tomore efficiently operate at the second frequency. The one or moreprocessor may also be configured to cause de-coupling of the secondconductive segment from the first conductive segment in conjunction withinstructing the feeding element to generate current with the firstfrequency instead of the second frequency, thereby allowing the antennaelement 1002 to more efficiently operate at the first frequency again.In some embodiments, the one or more processors are configured todetermine whether to causing the coupling (or de-coupling) of theseconductive segments based on information received from a receiver (e.g.,RX 104 or 704) that identifies a frequency at which the receiver isconfigured to operate (e.g., for larger devices with longer receivingantennas, this frequency may be 900 MHz, while for smaller devices withsmall receiving antennas, this frequency may be 2.4 GHz).

In some embodiments, the coupling described here in FIG. 10 can beimplemented by directly connecting two different segments of a singleantenna element 1002 while bypassing the conductive line locatedin-between the two connection points or the two different segments. Insome embodiments, coupling can be implemented between more than twodifferent segments of the antenna element 1002. The coupling of thedifferent portions or segments of a single meandered line antennaelement 1002 can effectively change the size or length of the conductiveline of the antenna element 1002, and therefore enable the singleantenna element 1002 to operate at different frequencies. The singleantenna element 1002 may also operate at more than one frequency bandsas a multi-band antenna.

All of these examples are non-limiting and any number of combinationsand multi-layered structures are possible using the example structuresdescribed above.

Further embodiments also include various subsets of the aboveembodiments including embodiments in FIGS. 1-10 combined or otherwisere-arranged in various embodiments, as one of skill in the art willreadily appreciate while reading this disclosure.

The terminology used in the description of the invention herein is forthe purpose of describing particular embodiments only and is notintended to be limiting of the invention. As used in the description ofthe invention and the appended claims, the singular forms “a,” “an,” and“the” are intended to include the plural forms as well, unless thecontext clearly indicates otherwise. It will also be understood that theterm “and/or” as used herein refers to and encompasses any and allpossible combinations of one or more of the associated listed items. Itwill be further understood that the terms “comprises” and/or“comprising,” when used in this specification, specify the presence ofstated features, steps, operations, elements, and/or components, but donot preclude the presence or addition of one or more other features,steps, operations, elements, components, and/or groups thereof.

It will also be understood that, although the terms “first,” “second,”etc. may be used herein to describe various elements, these elementsshould not be limited by these terms. These terms are only used todistinguish one element from another. For example, a first region couldbe termed a second region, and, similarly, a second region could betermed a first region, without changing the meaning of the description,so long as all occurrences of the “first region” are renamedconsistently and all occurrences of the “second region” are renamedconsistently. The first region and the second region are both regions,but they are not the same region.

The foregoing description, for purpose of explanation, has beendescribed with reference to specific embodiments. However, theillustrative discussions above are not intended to be exhaustive or tolimit the invention to the precise forms disclosed. Many modificationsand variations are possible in view of the above teachings. Theembodiments were chosen and described in order to best explain theprinciples of the invention and its practical applications, to therebyenable others skilled in the art to best utilize the invention andvarious embodiments with various modifications as are suited to theparticular use contemplated.

What is claimed is:
 1. A radio frequency (RF) charging pad, comprising:one or more processors for monitoring an amount of energy that istransferred from the RF charging pad to an RF receiver of an electronicdevice; and one or more transmitting antenna elements that areconfigured to communicate with the one or more processors fortransmitting RF signals to the RF receiver of the electronic device,each respective transmitting antenna element including: a conductiveline forming a meandered line pattern; an input terminal at a first endof the conductive line for receiving current that flows through theconductive line at a frequency controlled by the one or more processors;and a plurality of adaptive load terminals, distinct from the inputterminal and distinct from each other, at a plurality of positions ofthe conductive line, each respective adaptive load terminal of theplurality of adaptive load terminals coupled with a respective componentthat is configured to be controlled by the one or more processors and isconfigured to allow modifying a respective impedance value at eachrespective adaptive load terminal, wherein the one or more processorsare configured to adaptively adjust at least one of the frequency and arespective impedance value at one or more of the plurality of adaptiveload terminals to optimize the amount of energy that is transferred fromthe one or more transmitting antenna elements to the RF receiver of theelectronic device.
 2. The RF charging pad of claim 1, wherein thefrequency is in a first frequency band, and at least one of the one ormore transmitting antenna elements is configured to operate at a secondfrequency band based on adaptive adjustments, by the one or moreprocessors, to respective impedance values at one or more of theplurality of adaptive load terminals of the at least one transmittingantenna element.
 3. The RF charging pad of claim 1, further comprisingan input circuit that is coupled with the one or more processors and isconfigured to provide the current to the input terminal at the first endof the conductive line, wherein the one or more processors areconfigured to adaptively adjust the frequency by instructing the inputcircuit to generate the current with a new frequency that is distinctfrom the frequency.
 4. The RF charging pad of claim 3, wherein the oneor more processors are configured to adaptively adjust the frequency byinstructing the feeding element to generate the current with a pluralityof different frequencies that are determined using predeterminedincrements.
 5. The RF charging pad of claim 3, wherein: a respectiveconductive line for at least one of the one or more transmitting antennaelements has a respective meandered line pattern that allows the atleast one transmitting antenna element to efficiently transmit RFsignals having at least one of the frequency and the new frequency, atleast two adjacent segments of the respective conductive line having therespective meandered line pattern have different geometric dimensionsrelative to each other, and the respective conductive line has a lengththat remains the same when the at least one transmitting antenna elementis configured to transmit RF signals having at least one of thefrequency and the new frequency.
 6. The RF charging pad of claim 3,wherein: at least one transmitting antenna element of the one or moretransmitting antenna elements has a first segment and a second segment,the first segment including the input terminal, and the at least onetransmitting antenna element is configured to: operate at the frequencywhile the first segment is not coupled with the second segment, andoperate at the new frequency while the first segment is coupled with thesecond segment; and the one or more processors are configured to couplethe first segment with the second segment in conjunction withinstructing the feeding element to generate the current with the newfrequency that is distinct from the frequency.
 7. The RF charging pad ofclaim 1, wherein the one or more processors are configured to:adaptively adjust at least one of the frequency and a respectiveimpedance value associated with a first transmitting antenna element ofthe one or more transmitting antenna elements to cause the firsttransmitting antenna element to operate in a first frequency band, andadaptively adjust at least one of the frequency and the respectiveimpedance value associated with a second transmitting antenna element ofthe one or more transmitting antenna elements to cause the secondtransmitting antenna element to operate in a second frequency band,wherein the first frequency band is distinct from the second frequencyband.
 8. The RF charging pad of claim 1, wherein the electronic deviceis placed in contact with or close to a top surface of the RF chargingpad.
 9. The RF charging pad of claim 1, wherein the respective componentis a mechanical relay coupled with the respective adaptive load terminalfor switching the respective adaptive load terminal between open andshort states, and the impedance value is adaptively adjusted at therespective adaptive load terminal of the respective transmitting antennaelement by opening or closing the mechanical relay to switch between anopen or short circuit, respectively.
 10. The RF charging pad of claim 1,wherein the respective component is an application-specific integratedcircuit (ASIC), and the respective impedance value is adaptivelyadjusted by the ASIC to within a range of values.
 11. The RF chargingpad of claim 1, wherein the one or more processors are configured to:adaptively adjust at least one of the frequency and the respectiveimpedance value by adaptively adjusting the frequency and a respectiveimpedance value at one or more of the plurality of adaptive loadterminals to determine a relative maximum amount of energy that istransferred to the RF receiver of the electronic device, and once themaximum amount of energy is determined, cause each of the one or moretransmitting antenna elements to respectively transmit the RF signals ata respective frequency and using a respective impedance value thatresulted in the maximum amount of energy transferred to the RF receiver.12. The RF charging pad of claim 1, wherein the one or more processorsmonitor the amount of energy that is transferred to the RF receiverbased at least in part on information received from the electronicdevice, the information identifying energy received at the RF receiverfrom the RF signals.
 13. The RF charging pad of claim 12, wherein theinformation received from the electronic device identifying receivedenergy is sent using a wireless communication protocol.
 14. The RFcharging pad of claim 13, wherein the wireless communication protocol isbluetooth low energy (BLE).
 15. The RF charging pad of claim 1, whereinthe one or more processors monitor the amount of energy transferredbased at least in part on an amount of energy that is detected at therespective adaptive load terminal.
 16. A method of charging anelectronic device through radio frequency (RF) power transmission, themethod comprising: providing a charging pad that includes a transmittercomprising one or more RF antennas, wherein each RF antenna of the oneor more RF antennas comprises: a conductive line forming a meanderedline pattern; an input terminal at a first end of the conductive linefor receiving current that flows through the conductive line at afrequency controlled by one or more processors; and a plurality ofadaptive load terminals, distinct from the input terminal and distinctfrom each other, at a plurality of positions of the conductive line,each respective adaptive load terminal of the plurality of adaptive loadterminals coupled with a respective component that is configured to becontrolled by the one or more processors and is configured to allowmodifying a respective impedance value at each respective adaptive loadterminal; transmitting, via the one or more RF antennas, one or more RFsignals; monitoring an amount of energy that is transferred via the oneor more RF signals from the one or more RF antennas to an RF receiver;and adaptively adjusting a characteristic of the transmitter using theone or more processors of the transmitter to optimize the amount ofenergy that is transferred from the one or more RF antennas to the RFreceiver, wherein the characteristic is selected from a group consistingof (i) a frequency of the one or more RF signals, (ii) an impedance ofthe transmitter, and (iii) a combination of (i) and (ii), and furtherwherein the impedance of the transmitter is adaptively adjusted at arespective one or more of the plurality of adaptive load terminals ofthe one or more RF antennas using the one or more processors of thetransmitter.
 17. The method of claim 16, wherein the frequency is in afirst frequency band, and at least one of the one or more RF antennas isconfigured to operate at a second frequency band based on adaptiveadjustments, by the one or more processors, to respective impedancevalues at one or more of the plurality of adaptive load terminals of theat least one RF antenna.
 18. The method of claim 16, wherein: arespective conductive line for at least one of the one or more RFantennas has a respective meandered line pattern that allows the atleast one RF antenna to efficiently transmit the one or more RF signalshaving at least one of the frequency and a new frequency, at least twoadjacent segments of the respective conductive line having therespective meandered line pattern have different geometric dimensionsrelative to each other, and the respective conductive line has a lengththat remains the same when the at least one RF antenna is configured totransmit the one or more RF signals having at least one of the frequencyand the new frequency.
 19. The method of claim 16, wherein: at least oneRF antenna of the one or more RF antennas has a first segment and asecond segment, the first segment including the input terminal, and theat least one RF antenna is configured to: operate at the frequency whilethe first segment is not coupled with the second segment, and operate ata new frequency while the first segment is coupled with the secondsegment; and the one or more processors are configured to couple thefirst segment with the second segment in conjunction with instructing afeeding element at the input terminal to generate the current with thenew frequency that is distinct from the frequency.
 20. A non-transitorycomputer-readable storage medium comprising executable instructionsthat, when executed by one or more processors that are coupled with aradio frequency (RF) charging pad that includes one or more transmittingantenna elements, cause the one or more processors to: monitor an amountof energy that is transferred from the RF charging pad to an RF receiverof an electronic device; communication with the one or more transmittingantenna elements for transmitting RF signals to the RF receiver of theelectronic device, each respective transmitting antenna elementincluding: a conductive line forming a meandered line pattern; an inputterminal at a first end of the conductive line for receiving currentthat flows through the conductive line at a frequency controlled by theone or more processors; and a plurality of adaptive load terminals,distinct from the input terminal and distinct from each other, at aplurality of positions of the conductive line, each respective adaptiveload terminal of the plurality of adaptive load terminals coupled with arespective component that is configured to be controlled by the one ormore processors and is configured to allow modifying a respectiveimpedance value at each respective adaptive load terminal; andadaptively adjust at least one of the frequency and a respectiveimpedance value at one or more of the plurality of adaptive loadterminals to optimize the amount of energy that is transferred from theone or more transmitting antenna elements to the RF receiver of theelectronic device.